This study compares the effects of the most commonly used pesticides (mainly organophosphate compounds) on eggs and birds of several avian species. We are comparing effects on domestic birds (chickens) with those on three wild species; quail, pheasants and chukar partridges. Levels of tolerance to a variety of pesticides, commonly used by agricultural industries, have been established in feeding, in egg injection and egg spraying trails, and the major conclusions from the comparisons of resistance of the different species and routes of administration are available. One water-soluble compound (Azodrin) and two fat-soluble compounds (Thimet and Trithion) were chosen for a more detailed analysis. Azodrin is highly toxic at low levels and, when injected, produces consistent embryonic abnormalities. Dissatisfaction with conventional egg injection methods led us to begin work on alternative assay methods; direct application onto the embryo, and by CAM (chorioallantoic membrane) grafting. During the feeding trials, it was noticed that adult Bobwhite quail showed both a much greater than average resistance than other species and also considerable variability in response to the level of pesticide fed. Accordingly this species is being used for genetic studies of pesticide susceptibility. Analysis of effects of pesticides applied topically are underway using normal birds (White Leghorns), and two mutant lines of birds; one lacking feathers and other epidermal derivatives (scaleless), and one with a form of ichthyosis (thick scale-like skin). Azodrin (water-soluble) and Thimet and Trithion (oil-soluble) were selected for this study, which also explores the effects of oil carriers on skin with analyses at the light and fine structural levels.